1. Field of the Invention
The present invention relates to a barrier electrode for the treatment of surfaces of electronically conductive or non-conductive materials with medium frequency electric discharges. The present invention also relates to a barrier electrode arrangement with one or more such barrier electrodes.
2. Description of the Related Art
Barrier electrodes are used in surface technology in an arrangement of single or double barrier electrodes for treating the surfaces of electrically conductive or non-conductive materials. The rod-shaped barrier electrode to which high voltage is applied is usually arranged opposite a counter electrode. The counter electrode is provided either with or without a dielectric barrier. Cylinder as well as plate geometries are used for the counter electrode. The counter electrode is electrically switched to ground potential. The material to be treated (substrate) is placed closely on the grounded counter electrode and forms relative to the high voltage electrode a gap of a few millimeters across which the barrier discharge is ignited.
German Gebrauchsmuster 94 023 70 discloses an electrode for corona treatment which is composed of a metal core provided with an electrical sheathing. The metal core has throughbores for conducting a cooling medium therethrough. An electrode constructed in this manner is arranged parallel to the counter electrode which in most cases is cylindrical.
EP 0 621 667 discloses an electrode which is composed of an oblong hollow copper body which is provided with a dielectric on at least that surface which is located opposite the counter electrode. Liquid is conducted through the hollow electrode for cooling the electrode.
In the barrier electrodes described above and in other barrier electrodes, whether they have a dielectric-coated metal core or hollow body or a dielectric profile with metal core, sliding discharges occur at the electrode sides in dependence on the applied voltage.
Depending on the applied voltage, the sliding discharges may reach the support components; this leads to damage after a short period of time and to a failure of the plant for the surface treatment. Moreover, the sliding discharges have a spark-like or filament-like discharge character with channels with high current density. The high current density leads to an undesirable thermal heating of the electrode system and of the material to be treated. The filament-like discharge character can additionally lead to a non-uniform surface treatment. In the case of sensitive substrates which are usually thin, local damage may also occur on the surface due to thermal overheating. Consequently, the electrical energy which has been supplied is partially converted into heat which is not utilized.
The following problems occur at least to some extent in the known barrier electrodes:
the structural configuration results in sliding discharges which lead to a destruction of the support components;
sliding discharges are the cause of thermal loads on the electrode and on the material to be treated; this makes it necessary to cool the electrode;
the coating on the metal carrier develops microscopic cracks over time due to the thermal expansion; this results in an electric short circuit which leads to a failure of the treatment station and, thus, to a stoppage of the production;
a supply of processed gas is not provided.
Therefore, it is the primary object of the present invention to provide a barrier electrode and an arrangement of barrier electrodes of the above-described type in which the problems mentioned above do not occur and especially the disadvantageous sliding discharges are prevented.
In accordance with the present invention, the barrier electrode is constructed as a tube of dielectric material with two ducts extending parallel to each other in the longitudinal direction of the tube, wherein the duct which in the position of use faces the counter electrode is provided with a high voltage conductor, and wherein the other second duct serves for supplying a temperature-influencing medium or a process gas.
Consequently, the barrier electrode according to the present invention practically is composed completely of dielectric material in the form of a tube provided with two ducts. The two ducts are arranged so as to extend parallel to the counter electrode, wherein the duct facing the counter electrode contains the high voltage conductor. A temperature-influencing medium or a process gas flows through the duct facing away from the counter electrode.
Sliding discharges cannot occur in such a configuration.
In accordance with an advantageous feature, the high voltage conductor is a flat component and is arranged parallel to and on the inner surface of the first duct which faces the counter electrode in the position of use.
In accordance with another advantageous feature, the discharge surface which in the position of use faces the counter electrode is provided with a surface corrugation in order to improve the ignition.
It is also possible to form the high voltage conductor which is arranged in the first duct facing the counter electrode by a filling of metal granulate.
If the high voltage conductor is constructed flat, it is advantageous to fill the remaining hollow space with a dielectric granulate.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.